esa’s darwin space interferometer huub röttgering sterrewacht leiden

ESA’s Darwin space interferometer

Huub RöttgeringSterrewacht Leiden

The InfraRed Space InterferometerDARWIN

• 2014• 6 1.5 m telescopes• Hexagonal configuration• Beam combiner• Passive cooling (40 K): 5-20 micron

Ringberg, 5-Sept-2003 Imaging with Darwin

Overview

Introduction– Timeline / status project– Relation with NASA’s Terrestrial Planet

Finder Imaging considerations Science


Finding and characterising exo-Earth’s– Nulling interferometry

Science

The Problem

Detecting light from planets beyond solar system is hard:– Planet emits few

photons/sec/m2 at 10 m– Parent star emits 106 more– Planet within 1 AU of star– Dust in target solar

system 300 brighter than planet

Finding a firefly next to a searchlight on a foggy night


Finding and characterising exo-Earth’s– Nulling interferometry– Atmosphere -> CO2

– Wet and pleasant H20– Life O3 (? / !)

High resolution and sensitive IR imaging– Cophasing using an off-axis reference star

Science

CO2

O3

H2O

(m)

6 8 10 12 14 16 18

Earth at 10pc


Darwin timeline 1993: Léger et al

– ``Darwin proposal’’ 2000 Presentation Alcatel system level study 2004 Results significant technology development

program (15 Meuro)– Optical components, coolers, thrusters, metrology,

control software, 2 breadboards … 2007 – SMART2 techno demonstration flight

– (mainly LISA technology) 2010 – SMART3 techno demonstration flight

– 2-3 space craft 2014 – launch


NASA’s TPF

Similar goals and timelines

1999:

IR interferometer with cooled 4x3.5 m mirrors and ~75-1000 m baseline

Vegetation edge

Blue sky

Earthspectrum

fromEarth-shine

2000

Variable-Pupil Coronagraph IR Nulling Interferometers

Large Aperture IR Coronagraph

SVS

coronagraphe

M2

M3

M1

Hyper-telescope

2001: 4 different studies

Variable-Pupil Coronagraph

IR Nulling Interferometers

•Coronagraph – Difficult•10-15 meter mirror with rms surface ~< 1 Å

–Deformable mirrors - control to <1 Å rms over wide range of scales

–Wavefront sensing - adequate for <1 Å control

•Interferometer - Complex–Cryogenic nulling - 10-5 or 10-6 depth across ~1 octave

–Wavefront & amplitude control - spatial filter in mid-IR (+ DM for low spatial freqs) + control of thermal & vibration effects + acc. amplitude measurement

–Beam transport issues (rejection of stray light at small angles)

2002: down selection for 2 concepts


Joined ESA/NASA mission MOU: aims for a joining in 2006 Plan

– Both sides continue technical studies– Regular scientific contact– Criteria to guide continuation after 2006

• #1: Sensitivity in finding and characterizing exoplanets• #2: Richness of astrophysical science opportunities• #3: Technology development needed• #4: Life-cycle costs• #5: Risk of cost, technology, schedule, on-orbit failures• #6: Reliability and robustness


Astrophysical imaging with Darwin

1. Imaging considerations2. Science

Röttgering et al. 2003, Heidelberg conference


Imaging performance at 10 micron

Sensitivity (Takajima and Matshura, 2001)• Limited by shot noise from the zodiacal background.• Similar to JWST

– Point source sensitivity• 1 hour, s/n=5: 2.5 microJy

– Image sensitivity • S_integrate/noise > 50 within FOV• > 2.5 microJy for a 100 hour

Resolution– Baselines up to 500 meter– 200 m baseline: 10 mas

• JWST 350 mas


Imaging considerations

PSF of an individual telescope: 1.4 arcsec– = maximum FOV for pupil combination

Mapsize (200 m baseline/telescope diameter) <~ 100 * 100 independent pixels

Complexity– per configuration maximum 6*5/2 = 15 uv points– number of uv-points >>~ number of image

parameters– for a complex map of 100 * 100 independent pixels:

• >>~ 666 configurations


Baseline dynamics

Fastest reconfiguration cycle takes about 16 hours

Snapshots will be taken “on the fly”

Basic reconfiguration approach

a single expansion up to baselines of 500 m and

contraction coupled to a 60o rotation

bang-bang thrust profile both radially and tangentially

<dB/dt> = 1.5 cm/s @ 1 mN

16

d’Arcio et al. 2001


UV coverageHexagonal array -> 9 independent visibilities per snapshot 600 snapshots, ~ 5400 uv points/reconfiguration cycle

-> Filling the UV plane is ’’easy’’ Ground based telescopes are ``fixed’’ (radio) Baseline/apertureis huge

17

d’Arcio et al. 2001


Issue: Cophasing How to phase-up the array not using the target?

– Essential to• integrate longer than the coherence time of the interferometer

(~10 sec)• Measure complex visibilities (Amplitude and phase) needed for

imaging– Off-axis bright stars (there are enough!)

• Similar to PRIMA instrument for the VLTI (Quirrenbach, this meeting)

• Multiplexing in wavelengths has the advantage that science and reference beams travel along common path (Alcatel)

– Implementation1. Modification to the nulling beamcombiner (Alcatel)2. Separate imaging beamcombiner

How to get a large Field of View?– Mosaicing

• Expensive in time– homothetic mapping

• Relative complex• Pupil matching in

magnification and orientation before image plane combining

• Implementation

– Pupil matching/zooming optics at central beamcombiner

– Pupil matching/zooming at telescopes

(see d’Arcio and le Poole, 2003)

positioning stages

4kx4k detector

imaging telescope

Zoom optics(5-50x)

Light f rom telescope

Afocal zoomoptics (5-50x)

Lo

(fi xed)


conventionalpupil mapping

variable magnification

positioning stages

4kx4k detector

imaging telescope

Zoom optics(5-50x)


Afocal zoomoptics (5-50x)

Lo

(fi xed)


conventionalpupil mapping

variable magnification

Physical processes observable at 6-20 micron– Molecules: Rotational and

vibrational lines • Temperatures, densities,

kinematics, Chemistry

– Ions: Forbidden fine-structure lines• Temperatures, densities,

kinematics, abundance's

– Dust: PAH features, continuum shape• Composition, temperature

– Late type stars: continuum (high z)• Spatial scales

ISO observationsStarburst galaxy

Circinus


Appropriate sensitivity and angular resolution ?

Star and planet formationAGN

Distant galaxies

Star and Planet formation

Sketch of scenario maybe in place (Shu et al. 87)

Vast range of conditions and relevant timescales– densities 10^4 - 10^13

/cm^3– temperatures 10 - 10,000 K – month - 10^6 years

Issues– density, temperature and

dynamical structure of disks?

– At what stage and when do planets form?

Compendium of Monnier and Millan-Gabet of K-band sizes of YSOs

Disk models of D’Alessio, Merin

An unphysical, unrealistic extrapolation-> fainter YSO are small (10-100 mas ?)

Log

Rad

ius[

mas

]

4

2

0-2 -1 0

Log flux @ 14 micron [Jy]

ISOCAM survey of your starclusters at 6.6 and 14.3 micron (Eiroa et al)

Darwin

MIDI


Active galactic Nuclei Zoo: Seyfert, Starburst

quasars ... – unification: orientation,

time-evolution, mass, spin

1000 times more AGN at z=2 than z=0

Every galaxy has a central massive Blackhole (?)

Issues:– Physics? When and how

do BH form?– Relation to Galaxy

formation?


AGN may contain dusty tori– can obscure the central QSO– feeds the massive Black Hole

Radiative transfer model of a dusty torus – size scales with QSO

luminosity– SED from = 1 - 300 m– morphologies at = 10 m

Models of Tori of Granato et al.

Adapted to NGC 1068, Heijligers etal.

Darwin observations of Tori D = 300 times the sublimation radius

NGC1068:

– Bight, low luminosity nearby AGN

• ~10 Jy: prime target for MIDI/VLTI in 2003

• 1.7 1031 erg/s/Hz at = 10 m

– (prime target for MIDI/VLTI in 2003)

Weak AGN observable up to z = 1 - 2

Stronger AGN up to z = 10NGC1068

0.01 0.1 1 10 redshift

1’’

0.1’’

0.01’’

50 Jy

5 JyL (

10

m [

1030

erg

/s/H

z]

Distant Galaxies When and how do galaxies form?

– Star formation history, galaxies shapes– Relation to black hole formation

8-10 meter telescopes: a few thousand with 3<z<6 and still counting– Hardly morphological information

Darwin: morphologies of the older stellar component– observe 2 micron rest == 10 micron for z=4

Semi-analytical models of galaxy formation as guidance – input: evolution of cold-dark matter halos, prescriptions for cooling, star

formation and feedback, dust…– output: large samples of mock galaxies and their properties (SF, mass,

type)

FIRES survey IsaacVLT

: 2.5^2 arcmin 96 h in J, H, K

HDFS limit in K = 24.4

mag Image HST

I+H+K Franx, Labbe,

Forster,schreiber, Rix, Rudnick, Röttgering, etal.


SED fittingwith galaxy templates

•Photometric redshift•Estimate 10 micron flux density

Rudnick, Labbe et al.


JWST resolutionAt 10 micron(0.35 arcsec)


100 hour, S_int/noise=50

F (

10

m )

J

y

(photometric) redshift

100 hourPointsource S/N=5


Conclusion

Darwin will be a powerful instrument for – Finding and characterizing exo-Earth– Astrophysical studies

Sensitivity is similar to JWST– Cophasing is an important issue

Size scales, AGN, YSOs, distant galaxies are appropriate– Case for larger fields

2025Terrestrial planet imager?20 8-m telescopes

esa’s darwin space interferometer huub röttgering sterrewacht leiden

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